Main Effect
- Measures the average effect of a single variable on an outcome across all levels of other variables.
- Does not account for the influence of other variables; consider potential confounders or moderators when interpreting it.
Definition
Section titled “Definition”The main effect is the overall impact or effect of one variable on a dependent variable, without taking into account the potential influence of other variables. It is the average effect of a single variable across all levels of other variables.
Explanation
Section titled “Explanation”A main effect summarizes how one predictor (independent variable) relates to an outcome (dependent variable) when averaging over the other variables in the analysis. It captures the general direction and magnitude of that single variable’s association with the dependent variable but ignores any conditional relationships that might arise from other variables.
Examples
Section titled “Examples”Example 1: The main effect of study time on exam performance
Section titled “Example 1: The main effect of study time on exam performance”A study measures study time (in hours) and exam performance (in points) for 100 students. On average, students who study more tend to score higher on the exam. The main effect of study time on exam performance is positive, indicating that increased study time is associated with higher exam performance. This main effect does not take into account other variables such as intelligence, motivation, or study skills, which may also influence exam performance.
Example 2: The main effect of gender on salary
Section titled “Example 2: The main effect of gender on salary”A study measures gender and salary for 100 employees. On average, male employees earn higher salaries than female employees. The main effect of gender on salary is positive for males and negative for females, indicating that being male is associated with higher salaries while being female is associated with lower salaries. This main effect does not account for other variables such as job title, education, or experience, which may affect salary.
Notes or pitfalls
Section titled “Notes or pitfalls”- A main effect does not account for the potential influence of other variables (for example: intelligence, motivation, study skills, job title, education, experience).
- Because other variables may influence the relationship between the independent and dependent variables, it is important to consider those variables when interpreting a main effect.
Related terms
Section titled “Related terms”- Independent variable
- Dependent variable